Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Swiss drug maker Roche alerted the Food and Drug Administration last November about reports of the disease in patients taking its drug CellCept, which is used to avoid rejection in organ transplant patients.

FDA said Thursday it is looking into similar risks with Myfortic, a drug made by fellow Swiss drugmaker Novartis that is used to prevent kidney transplant rejection.

The agency said it will take about two months to review the reports and consider new labeling for the medications. Until then, regulators advise doctors and patients to watch for symptoms of neurological problems.

The disease, known as progressive multifocal leukoencephalopathy, attacks the brain and central nervous system and is usually fatal. Symptoms include vision problems, loss of coordination and memory loss. Patients who survive are often permanently disabled, according to the FDA.

Roche has confirmed 10 cases of the disease in CellCept patients, according to company spokesman Christopher Vancheri. He added that the drug has been used by more than 500,000 patients since 1995, when it was approved in the U.S.

CellCept was Roche's sixth best-selling drug last year with sales of $1.99 million.

Roche submitted new labeling for CellCept last November. The FDA is still reviewing it.

European regulators have already added language about the disease to CellCept. In February, Roche sent a letter to European doctors, highlighting the changes. The letter said problems were reported in kidney, heart and lung transplant patients. The disorder was also seen in patients taking the drug for a form of lupus, a use that is not approved by regulators.

Roche said that it is difficult to sort out the role of its drug in the reports, since many patients had other diseases and were taking other drugs. "However, the contributory role of CellCept cannot be excluded," states the letter, which FDA posted to its Web site Thursday.

A spokeswoman for Novartis said the company is unaware of any instances of the neurological disease in patients taking its drug and plans to cooperate with any labeling changes recommended by regulators.